1. Field of the Invention
The present invention relates to a wood type golf club head.
2. Description of the Related Art
Generally in a golf club head, the back spin amount of a shot tends to change depending on the position of the impact point on the face portion. For example, in a wood type golf club head, if the position of the impact point is higher than the sweet spot, the back spin amount tends to decrease. If the impact point is at a position lower than the sweet spot, the back spin amount tends to increase.
To reduce the difference in the back spin amount generated by the vertical variation in the impact point position, a face portion having areas of difference surface roughnesses has been proposed. Golf club heads described in Japanese Utility Model Laid-Open No. 60-25654, Japanese Patent Laid-Open No. 62-144674, Japanese Patent Laid-Open No. 9-047530, and U.S. Patent Application Publication No. 2004/0038745 are based on an idea that the back spin amount can be increased by increasing the surface roughness of the face.
On the other hand, in a golf club head having a relatively small loft angle (for example, 20° or less), in some cases, the higher the surface roughness is, the lower the back spin amount is. A golf club head described in Japanese Patent Laid-Open No. 2004-201787 is based on an idea that the roughness of the face is decreased at a position where the back spin amount decreases, and the roughness of the face is increased at a position where the back spin amount increases. That is, the golf club head is based on an idea opposite to that of Japanese Utility Model Laid-Open No. 60-25654, Japanese Patent Laid-Open No. 62-144674, Japanese Patent Laid-Open No. 9-047530, and U.S. Patent Application Publication No. 2004/0038745.
In the wood type golf club head, since the loft angle is relatively small, it is effective to decrease the roughness of the face at a portion to increase the back spin amount and increase the roughness of the face at a portion to decrease the back spin amount, as described in Japanese Patent Laid-Open No. 2004-201787.
As a method of adjusting the surface roughness of the face portion, a process such as sand blast or shot peening is known. However, to implement a change in the surface roughness of the face portion as designed, the process may be difficult or may need effort. As another method of adjusting the surface roughness of the face portion, contriving score lines is considerable. However, in, for example, a golf club head for games, it is difficult to implement a change in the surface roughness of the face portion as designed in terms of conformity to rules (R & A rules).